Bearing assemblies having at least two parts moving against each other are often supplied with a lubricant for aiding the movement of the parts against each other. The lubricant may be self-contained between the moving parts, for example, by sealing lubricant between the moving parts using at least one sealing element. In some bearing assemblies, lubricant may be constantly or intermittently supplied from a lubricant source to an interface between the moving parts.
Some bearing assemblies include moving parts provided with interfacing reduced-friction surfaces. Reduced-friction surfaces may include diamond, diamond-like carbon, disulfides, and/or carbides, for example. Further, reduced-friction surfaces may be applied as a coating (applying a layer of the reduced-friction material over an outer surface of an already formed part) or may be formed as an outer surface of a part, for example, by polishing or by forming the outer surface of the part with a reduced-friction material during manufacturing or making of the part.
An example of a bearing assembly is a bearing package provided in a rotating control device (RCD) for use during downhole drilling operations. An RCD (also referred to as a rotating control head, RCH) includes a bearing and sealing assembly that enables rotation of a drill string and longitudinal motion of a drill string as a wellbore is drilled, while maintaining a fluid-tight seal between the drill string and the wellbore so that drilling fluid discharged from the wellbore may be discharged in a controlled manner. By controlling discharge of the fluid from the wellbore, a selected fluid pressure may be maintained in the annular space between the drill string and the exterior of the wellbore.
RCDs may be provided along a casing or riser assembly, through which the drill string may be inserted and rotated during the drilling operations. A bearing package may be provided within the RCD to allow rotation of the drill string through one or more sealing or packing elements in the RCD, where the bearing package and sealing element(s) together seal-off drilling fluids from moving through the RCD. An RCD bearing package may include an inner rotatable part commonly referred to as a drive ring or a quill and an outer stationary part, which may be referred to as the outer housing or bearing housing. The interfacing surfaces between the drive ring and the bearing housing may include one or more reduced-friction surfaces. Further, RCD bearing packages may include lubricant provided between the interfacing surfaces of the drive ring and bearing housing to aid in rotation of the drive ring within the bearing housing.